Re: should there be an age for black belts?
Shodokan does not allow shodan or above to under 18s. In fact, you have to re-grade all the sylabus when you turn 18 -- sure, you generally get to 2/1 kyu on your first grading cause really you know most of it.
Remember that due to physionomy, under 16s should not use wrist locks. It can permanently damage said wrist.